Dewaxing oils with light hydrocarbons



Feb. 13, 1940. w, EDMONDS r 2,189,885

DEWAXING OILS WITH LIGHT HYDROCARBONS 7 Original Filed Sept. 18, 1951 2 Sheets-Sheet 2 Patented Feb. 13, 1940 PATENT OFFICE aisasss j newixmddmswnn LIGHT HYDROCARBONS William Edmonds, Scarsdale, N. Y., assignor to Standard Oil Development Company, a corporation of. Delaware Original application September 18, i98i, ;s ria1 No. 563,557; Divided and this application May 13, 1936, Serial No. 19,412-

,eolaiins; (oi. ice-18) This invention relates to the dewaxi'n'g'of oils, especially petroleum oils, in which the solvent used comprises liquefied normally gaseous hydro-- carbons such as ethane, propane, butane and similar hydrocarbons or mixtures thereof.

This application is a division of my' prior application Serial No. 563,557, filed on September 18, 1931, and is directed principally to the method of dewaxing in which the oil to be dewaxed is chilled to successively lower temperatures in a plurality of stages. 1

The invention will be fully understood from the following description read with reference to the accompanying drawings of which Fig; 1 is a semi-diagrammatic view in sectional elevation of the apparatus used in a batch operation, and n W Fig. 2 is a semi-diagrammatic view in sectional elevation of the apparatus used in a continuous operation.

The drawings willbe describedsimultaneously with the process. r i

In Fig. 1 numeral 1' designates ares'ervoir for the liquefied hydrocarbon gas such aspr'opane in admixture with butane, ethane, etc., 2' a mixing tank. The required amount of propane is dropped into the mixing tank 2 from reservoir 1' and is admixed with the'molten waxy charging stock admitted throughvalved line 3' froma' reservoir (not shown). The closed steam line 4 serves to bring up the temperature of the propane to the required degree before the molten charge is admitted. The warm solution is then dropped into chiller 5'. The mixed charge iscooled by releasing propane vapors through valved line "I'.

The released vapors pass through heat exchanger 8' to the suction valve of the first compressor 9 The vapors arecompressed by 9' and then passed I through liquid propane inthe intercooler I0,

further compressed by compressor l l and finally condensed with water in the indirect condenser 7 is sufficient to cause their condensation at the 8 temperature of the cooling water. The, arrangements of pressuremand,compression rates are such that the temperature 6f the returned liquid propaneis only a few degrees higher than that in chiller 5. Sufiicient vapor is released by the expansion of the liquid propane into the chiller to' give some agitation which assists in keeping the contents of the chiller at a uniform temperature and concentration. However, if so desired, the chiller may beprovided with a mechanical agitator (not shown).

The chilled waxy oil andliquid propane mixture is settled in the chiller which is held at constant temperature and the supernatant liquor drawn ofi through valved line l4 into a still l5. li puinp [6' may be provided for this purpose. The sludge remaining in the chiller may be washed wth propane. For this purpose propane from the reservoir l' is flash cooled by expansion through line I If into the intercooler l0. Evolved vapors are compressed as before. The cold propane is then admitted to the chiller through float valve I3. Agitation incident to further expansion is sufiicient to mix it with the sludge. When settling is again completed this wash. liquor may be sent to still [5' or reserved for use as diluent with, or wash for, the next har 'lpirectly after decantation of the original supernantant liquor or after washing with the liquid propane, the sludge may be passed, by

means of pump 18'. through the filter press I9.

The filtrate is discharged through lines 20' and I4 into the-still Hi. The chiller maybe flushed out with the liquid propane and the wax in the press may also bewashed with the same. Filtration may be employed entirely to effect the separation by discharging the total chilled flux throughthe filter press. The recovered wax may be removed through tube 2|.

The dewaxed lubricating oil is separated from the propane and other light hydrocarbons by distillation under pressure in the still l5 provided with clcsed steam coils 22'. A column 23 is connected with the still and condensation of the vapors is efiected in water cooled condenser 24'. the liquefied propane being passed through line 25' to'cohtainer' I. 26 is a line for returning reflux to the column 23? and 21' is a discharge line for the .dewax'edlubricating oil. Various combinations of distillation and compression may be used for separating from the dewaxed oil the propane; and other light hydrocarbons and liquefying the same. i i V Itis apparent from the, above description that the liquid propane, pure orgadmixed with other liquefied hydrocarbons which are gaseous under all tial that all the liquid be returned in case an excess were provided at the start. This method of chilling may be termed auto' refrigeration. The rate of auto-refrigeration is controlled by the work done in the' compressor. or .com-' The latent heatof fusion of wax and pressors. the specific heat of the flux is removed by the vaporization of propane at ,auniform rate and an even temperature is 'a'ssuredhroughout the mass of the flux. The auto-regrigeration gives a much better control of the crystal formation than it is possible to obtain when heat is removed by indirect heat transfer fromthe body of a warmer liquid to a colder surface. Such indirect transfer requires that an appreciable ternp-erature difference beset up across the liquid which results in.shock chilling and irregular precipitation of the wax crystals. Also with this method of chilling, increasing the-capacity increases the temperature differenceand consequently the shock also increases with the capacity. With auto-refrigeration, however, rapid chilling can be accomplishedwithout shock, thus fixing the capacity of the chiller simplyby the time required for the crystalgrowth. This will result in considerable economy in the cost of the apparatus. Other highly volatile solvents may be used to receive the auto-refrigeration in place of the normally gaseous hydrocarbons here described, such as acetone, ether, sulfur, dioxide, ammonia, and thelike. It is generally preferable to use any of these solvents only in admixture with the normally gaseous hydrocarbons.

The wax crystals are not only uniformly sized.

due to the auto-refrigeration but also grow rapidly and without occlusion of oil, due to the fact that the viscosity of the flux is low, and, further, the solubilityof the wax in the flux is also small. The concentration of the liquid diluent is so regulated that the-gravity of the flux is between 60 and A. P, I. Under such conditions the flux hasa low-viscosity and the wax can be readily separatd therefrom.. The oil and diluent are completely miscible at the temperature of separation. The so-called wax inhibitors, such as asphalt, my be. removed along withthe wax, although it may provemore desirable toremove them by acid treating or other means. be-

fore the dewaxing. 1 a

-While anysuitable means, may be used to separate the wax or wax-asphalt precipitate from the blend, settling, filtration and a combination of the two have been employed. The conditions for settling are favorable due to the low vis cosity of the flux. Some waxes settle in a few. hours time to a sludge containing as much as 30% dry wax. In these cases decantation of the supernatant' liquor, 'andextraction of dissolved oil from the sludgeby mixing it with a succession of diluent washes," will give a practically eomplete separation of the oil from the Wax. The solid fraction so separated will contain not more than 10% of oil, as distinguished from wax, in that it is made up of compounds having melting points below 0 F. 4

'In other cases separation by settling may be' too slow or not complete. Filtration of the sludge may be employed in this case, followed by washing the wax in the press with cold diluent. For a given blend, the pour point of the oil recovered by settling and decantation will be the same as that recovered by filtration.

-...since' very rapid chilling by auto-refrigeration" may be efiected without resultant shook, my process lends itself to continuous operation in contra-distinction to other dewaxing processes "which are by'their nature batch processes. The

essential feature of the continuous operation conof a series of self cooled chillers operating zit-successively lower temperature and pressure levels. While it is possible to carry out the cooling in one step, multiple stage chilling is more desirable from-the point of the control of the process." The wax is separated by settling and washing although filtration may also be employed. In a variation of the process the washed wax sludge is continuously pumped to a recovery still to remove the light hydrocarbons therefrom. The dewaxed oil solution and the propane extract from the washers are separated into propane and dewaxed oil by distillation under pressure. The dewaxed oil may then be stripped with steam, or any other method to correct the flash. Iii-the multiple stage chilling of the continuous operation, the growth of the crystals may be controlled as to form in that the more desirable plate type of crystals which form in the first stage serve as nuclei for the smaller needles and other types which may come out in subsequent stages. It is also possible to chill a fraction of the total flux in one stage and use it for seeding the whole flux which may be chilled in successive stages. Such an operation would require a small chiller in parallel to the large multi-stage chillers. The concentration of the dilutent may be varied over wide limits from chiller to chiller in a multi-st'age unit, although the control of the operation is simpler when the concentration of of the diluent is not varied.

Referring to Fig. 2, numeral l designates the storage tank, for the oil to be dewaxed, 2 an overhead feed barrel for the oil, 3 the propane or other liquid hydrocarbon storage tanks, 4 and 5 the proportioning pumps for the oil and propane. The oil-propane mixture is passed through a steam heated mixer 6 and line 1 to the heat exchanger 8 in which the mixture is cooled and then discharged into the first chiller 9. The temperature of 9 is lowered by venting propane through valved line l0, compressing the propane vapors in the three-stage compressor ll, cooling the propane in cooler I2 and returning it through line IS in admixture with the oil-propane-mixture from line I to the chiller. The chilled flux is transferred through line M to the second chiller l5 which is again further chilled by venting propane vapors through valved line l6 to the intake valve of rotary vacuum pump l1, then compressing the vapors in the two-stage compressor l8, condensing them in condenser 19, and returning the liquid propane through the flash cooler and vapor separator 2|] and to the chiller l5. Uncondensed vapors are recycled from separator 20 to compressor l8 and condenser IS. The vapors may be withdrawn after leaving condenser l9 by means of valve line'fiil and returned to condenser I2. The fiux is then transferred from chiller l5 to the final chiller 2| which .is again cooled by venting propane vapors through line 22, and' the finally chilled flux then passes into the settling tank 23. Propane may be added waxed oil and propane mixture is drawn oiT from the settling tank through line 24 and passes by means of pump 25 through the heat-exchanger 8 and line 25 to the steam preheater 21 and thence to the fractionating column 28 of propane recovery still 29. The latter is heated by closed steam coil as. The light hydrocarbon solvent is distilled overhead, condensed in water condenser 3| and returned through overhead accumulators 32 and line 33 to the storage tanks 3. The oil residue from still 29 is further heated in steam preheater 3% and finally stripped from any remaining light ends in stripping still 35 by steam admitted through steam line 36. .The stripped dewaxed oil is then cooled in cooler 31 and passed to accumulators t8 and thence to the storage tank (not shown).

The wax sludge from settling tank 23 is pumped by means of pump 39 and line 40 through'the washer drum ll in counter-current with propane admitted from Fauto-refrigeration chiller 42 through line d3. The washed wax sludge is then pumped by 44 through line 45 and steam pre-' heater it to the column 41 ofthe wax stripping still 38. The stripped wax is removed therefrom throughbottoms line 49 and the propane vapors after condensation in water condenser 59 are passed through accumulators El and 52 and lines 53 and 33 to the propane storage tank. Column 51 is provided with water refluxcoils54. Pressure equalizing line 55 is provided between the propane storage tanks and the overhead accumulators 32.

The reflux obtained in gasoline stabilizers and containing. a large proportion of propane may serve as the light solvent in the process. The stabilizer reflux may be taken directly from tank wagons (not shown) :by line 56 and passed by rotary pump, 5? together with aqueous caustic soda solution from tank 58 to the washing c01 umn 59. The washed stabilized reflux is transferred from column 59 to the container 60 and hence into the storage tanks 3. The operation may be conducted in a manner by means of line 62 and chilled inthe small par.-

allel chiller 68. Portions of this chilled mixture containing small wax crystals are introduced into the feed lines of chillers 9, l5 and 21 by means of lines 65, M and 63 respectively. Propane is removed from the chiller 66 by means of line 61 and .introduced in the propane line l6.

The following example will illustrate my proc- A flux containing of a diluent having 121 A. P. I. gravityat 60 F. and 35% of a Mid- Continent overhead stock of 87 Saybolt viscosity at 210 F. and 113 F. pour point, was'chilled at 10 F./hr, by auto-refrigeration to .40 F.

.After settling'for 4 hours, 72% of the total volume was supernatant and was decanted from the t 3 sludge. This decanted liquor contained 0 F. pour lubricating equivalent-to 72.6% of the original stock/charged. Filtration and washing of the sludge yielded an additional 9.2% of 0 F.

pour lubricating oil and 18.4% of wa'xof melting point of F. by theA. S. method." The stock employed in the above experiment if deiwaxed by chillingin a naphtha flux and centrifuging, yields only 68% oil of 0 pour. In:

emotion of the abovedata on light hydrocarbon dewaxing shows that the sludge liquor is much less concentrated in oil than that which was de-' canted; This definit ly Shows a selective adsorption of the diluent such as propane on the surface of the crystals. On the other hand, where these.

crystals are formed in a heavier naphtha flux they adsorb oil which is consequentlylost when the wax is removed by centrifuging.

1. A process for separating wax from waxcontaining oil whichcomprises diluting the oil with a liquefied normally gaseous hydrocarbon successively lower levels in each chamber, 'sep arating the precipitatedwax from the oil-solvent mixture in the last chamber and removing the solvent from the dewaxed oil.

2. A method according to claim 3. A method according to claim 1 in which the solvent is a mixture of hydrocarbons of .2 and 3 carbon atoms.

4.'A method according to claim 1 in which 1 in. which the solvent is a hydrocarbon of 4 carbon atoms; 1

solvent, cooling the mixture to successively lower 1 wax separation temperatures in a plurality of separate chambers by reducing the pressure to the solvent is a liquefied hydrocarbon which has a vapor pressure higher than that of butane and lower than that of ethane. 1

5. .A method for separating wax from wax-con taining oil which comprisesdiluting the oil with a liquefied normally gaseous hydrocarbon, chilling the mixture to successively lower wax separation temperatures a plurality of separate stages, effecting the chilling at least partially by evaporation of a portion of the diluent, maintaining the ratio of diluent to flux substantially constant in each stage by condensing and recycling to the chillers that portion of the diluent which is evaporated, and separating the wax from the oil. I

6. A method for separating wax from wax-containing oil which comprisesdiluting the oil with a liquefied normally gaseous hydrocarbon, sep-" arately chilling a portion of the dilutedmixture to a temperature at which a small amount of wax is .caused to precipitate, adding this chilled portionto the remainder of the diluted mixture, chilling the same to a successively lower wax,

J. nnMoNns.

separation in a plurality of separate expansion stages, removing the wax so caused to precipitate, as i 

